There is conventionally known a single can-type composite heat source machine which comprises a single can body including a first combustion section having a first burner and a hot water supplying first heat exchanger located above the first burner, and a second combustion section having a second burner and a second heat exchanger located above the second burner and used for a purpose other than hot water supply, the first combustion section and the second combustion section being partitioned from each other by a partition wall and juxtaposed in a lateral direction (see, for example, Japanese Patent Publication No. H2-17784).
Furthermore, besides the composite heat source machine, a hot water supplying heat source machine is conventionally known which has an auxiliary heat exchanger of a latent heat recovery type which is located in an exhaust hood disposed on a top surface of a can body and which is connected to an upstream side of a hot water supplying main heat exchanger so that water vapor in an exhaust gas from a burner having passed through the main heat exchanger is condensed by the auxiliary heat exchanger and so that water to be supplied to the main heat exchanger is preheated in the auxiliary heat exchanger by means of the latent heat of the water vapor (see, for example, Japanese Patent Laid-Open No. 2004-198065). The thus provided auxiliary heat exchanger enables recovery of the latent heat, improving heat efficiency. Thus, the single can-type composite heat source machine desirably has the auxiliary heat exchanger to improve the heat efficiency.
Here, when the auxiliary heat exchanger is located in the exhaust hood, a guide plate inclined so that a rear part of the guide plate is higher than a front part thereof is generally provided in a lower part in the exhaust hood to divert the exhaust gas to a rear part in the exhaust hood and then to guide the exhaust gas forward. The auxiliary heat exchanger is located above the guide plate in the space in the exhaust hood. This configuration enables condensed water falling from the auxiliary heat exchanger to be received by the guide plate, preventing the condensed water from falling into the can body. Moreover, since the exhaust gas flows in a front-back direction with respect to the auxiliary heat exchanger, the height of the exhaust hood can be reduced. Furthermore, the auxiliary heat exchanger comprises a plurality of straight heat absorbing tubes provided in the exhaust hood so as to extend in the lateral direction between side plates arranged on the opposite lateral sides of the exhaust hood. The heat absorbing tubes are connected together on an outer surface of each of the side plates of the exhaust hood via U bents (U-shaped bent tube) each for two heat absorbing tubes. This constitutes continuous heat exchanging channels extending from upstream ends of the heat absorbing tubes to downstream ends of the heat absorbing tubes. Then, the water flowing through the heat exchanging channels is heated by the latent heat of the water vapor in the exhaust gas concentrated on the outer surface of each of the heat absorbing tubes.
Thus, when the single can-type composite heat source machine is configured to comprise the first and second auxiliary heat exchangers connected to the upstream sides of the first and second main heat exchangers, respectively, arranged in the upper part of the can body, the following configuration is generally adopted. Paired exhaust hoods for the first and second combustion sections are arranged on the top surface of the can body; each of the paired exhaust hoods has the guide plate in the lower part similarly to the above-described exhaust hood. A plurality of straight heat absorbing tubes constituting each of the auxiliary heat exchangers are laterally provided above the guide plate in the space in each of the exhaust hoods. The heat absorbing tubes are connected together, via the U bents each for two heat absorbing tubes, on the outer surface of each of the side plates arranged on the opposite lateral sides of the exhaust hood, to constitute the continuous heat exchanging channels.
However, this configuration requires the separate exhaust hoods for the first combustion section and the second combustion section, thus complicating the structure and increasing costs. Moreover, an installation space for the U bents needs to be provided between the exhaust hoods for the first combustion section and the second combustion section. Thus, the widths of both exhaust hoods needs to be increased outward in the lateral direction, thus increasing the size of an exhaust system.